The present invention relates to a semiconductor device, and in particular, to a semiconductor device having two or more IC modules which are stacked up into three-dimensional structure, in which both high speed operation and enough cooling capacity are realized.
Computers that are used in the field of scientific and technological calculations are being required to perform vast amounts of calculations with high accuracy and with high processing speed. Especially, requirements for speeding up of the processing speed are increasing every year. One known method for meeting the requirement is to shorten the lengths of signal lines which are connecting IC chips on a board. By shortening the signal lines, high packaging density is attained and thereby signal transfer speed between the IC chips is increased. However, such high-density packaging (in which the IC chips are packed closely) causes rapid increase of heat emission density from each IC chip, thereby the speeding up of processing speed becomes difficult. A semiconductor device which will be described below has been proposed in order to resolve the heat emission problem.
FIG. 1 is a schematic diagram showing an example of the composition of a conventional semiconductor device which is employed in supercomputers, parallel computers, etc. The conventional semiconductor device of FIG. 1 includes four semiconductor modules 80. Each semiconductor module 80 includes a motherboard 81 and a plurality of packages (one or two high-speed high-power CPU packages 82, memory (DIMM: Dual In-line Memory Module) packages 83, etc.) which are closely mounted on the motherboard 81. When the CPU package 82 is energized, large amounts of heat emission occurs and the speed and reliability of the CPU package 82 is affected by the heat. Therefore, an air-cooled metal heat sink 84 is attached to the top surface of each CPU package 82 in order to maintain the temperature of the CPU package 82 below an allowable temperature. The heat sink 84 has a plurality of radiating fins which are arranged at predetermined intervals. Forced-air cooling of the CPU packages 82 is carried out by use of an unshown cooling fan which blows air on the radiating fins of the heat sinks 84. The semiconductor modules 80 having such composition are mounted on a rack 85 in parallel and at even intervals.
Meanwhile, a water cooling system for a supercomputer has been proposed and disclosed in NEC technical report Vol. 39, page 36 (1986). In the technique of the document, a plurality of high-heat-emission LSIs are arranged in a two dimensional array on a ceramic base, and each LSI is provided with a water channel for cooling the LSI. The water cooling system could achieve some effect of permitting total heat emission of 3.3 kW (approximately 40 W per LSI).
In Japanese Patent Application Laid-Open No. HEI5-275584, a cooling device has been proposed in order to cope with the increase of heat emission density when CPUs (for portable devices) of low power consumption are mounted closely. In the cooling device which is designed to be applied to small-sized electronic equipment such as notebook computers, a plurality of IC chips are mounted on a motherboard and such motherboards are stacked so as to have three-dimensional structure. The key feature of the cooling device is its specific three-dimensional structure, in which the motherboards on which the IC chips are mounted are stood upright and plate-like heat pipes (whose inner walls are formed to have capillary structure) are placed between the motherboards so as to make thermal contact with the IC chips (or the motherboards).
The operation of the cooling device is as follows. When heat emitted by the IC chips is conducted to the plate-like heat pipe, coolant in the plate-like heat pipe evaporates and the evaporated coolant moves to a low-temperature part of the plate-like heat pipe as bubble current. The evaporated coolant (bubble current) reaches a heat sink which is provided to the upper end of the plate-like heat pipe, and the evaporated coolant which is cooled by the heat sink is condensed into liquid. The coolant condensed into liquid returns to heated part of the plate-like heat pipe (near the IC chips) by capillarity or gravity. The cycle (evaporation xe2x86x92movementxe2x86x92condensationxe2x86x92movementxe2x86x92evaporation) is repeated by the coolant and thereby heat transport and cooling is carried out continuously. By the employment of the thin plate-like heat pipes, packing volume of the semiconductor device is reduced and signal lines between the IC chips are shortened in comparison with the conventional air cooling system using air-cooled heat sinks.
However, the conventional techniques which has been explained above involve the following problems or drawbacks.
In the conventional semiconductor device of FIG. 1, the volume ratio of the air-cooled heat sinks in the semiconductor device is necessitated to be large, thereby signal lines for providing connection between IC chips are necessitated to be long. The long signal lines cause delay and attenuation of signals, thereby speeding up of the processing speed becomes impossible.
In the technique of NEC technical report Vol. 39, the water cooling mechanism is necessitated to be large-sized when three-dimensional packing structure is constructed. Therefore, packing volume of the three-dimensional structure can not be made compact similarly to the case of the conventional semiconductor device of FIG. 1.
In the case of the technique of Japanese Patent Application Laid-Open No. HEI5-275584, cooling capacity can not be increased more than over 10 watts per chip if three-dimensional packing structure is constructed by use of high-speed high-power chips (100W class power consumption) which are employed for high-performance computers. Therefore, the technique of the document can not be employed for the cooling of high-power chips in three-dimensional packing structure.
It is therefore the primary object of the present invention to provide a semiconductor device in which both high packing density (short signal lines between IC chips) and sufficient cooling capacity can be attained.
In accordance with a first aspect of the present invention, there is provided a semiconductor device, in which a semiconductor module is constructed by use of a wiring board, one or more IC chips which are mounted on the wiring board and which emit heat during their operation, and one or more heat sinks which are attached to the IC chips via a thermal-conductive adhesive and are forcedly cooled by a coolant flowing through channels which are formed therein, and two or more of such semiconductor modules are stacked up into three-dimensional structure.
In accordance with a second aspect of the present invention, in the first aspect, the wiring board of each semiconductor module is provided with sockets having I/O pins and concavities. Electrical connection between adjacent semiconductor modules of the semiconductor device is established by inserting the I/O pins of the sockets of one semiconductor module into the concavities of the sockets of the other semiconductor module.
In accordance with a third aspect of the present invention, in the first aspect, the channels in the heat sink are implemented by a plurality of channel grooves which are generated between a plurality of fins which are formed in a cavity inside the heat sink at predetermined intervals.
In accordance with a fourth aspect of the present invention, in the third aspect, the heat sink includes: a first metal block having the channel grooves and the fins; and a second metal block which is joined to the first metal block so as to cover the fins of the first metal block.
In accordance with a fifth aspect of the present invention, in the third aspect, each of the fins of the heat sink is provided with slopes at its both ends.
In accordance with a sixth aspect of the present invention, in the third aspect, the width of the channel groove in the heat sink is set to 0.05 mmxcx9c0.4 mm.
In accordance with a seventh aspect of the present invention, in the sixth aspect, the width of the channel groove in the heat sink is set to 0.2 mmxcx9c0.25 mm.
In accordance with an eighth aspect of the present invention, in the third aspect, the length of the channel groove in the heat sink is set to the length of the IC chip or more.
In accordance with a ninth aspect of the present invention, in the first aspect, the thickness of the heat sink is set to 1 mm or less.
In accordance with a tenth aspect of the present invention, in the first aspect, the semiconductor device further comprises a forcedly air-cooled radiator for cooling the coolant.
In accordance with an eleventh aspect of the present invention, there is provided a semiconductor device comprising two or more semiconductor modules which are stacked up into three-dimensional structure. The semiconductor module includes a wiring board, one or more IC chips which are mounted on the wiring board and which emit heat during their operation, and one or more heat sinks which are attached to some of the IC chips via a thermal-conductive adhesive and are forcedly cooled by a coolant flowing through channels which are formed therein.
In accordance with a twelfth aspect of the present invention, in the eleventh aspect, the wiring board of each semiconductor module is provided with sockets having I/O pins and concavities. Electrical connection between adjacent semiconductor modules of the semiconductor device is established by inserting the I/O pins of the sockets of one semiconductor module into the concavities of the sockets of the other semiconductor module.
In accordance with a thirteenth aspect of the present invention, in the eleventh aspect, the channels in the heat sink are implemented by a plurality of channel grooves which are generated between a plurality of fins which are formed in a cavity inside the heat sink at predetermined intervals.
In accordance with a fourteenth aspect of the present invention, in the thirteenth aspect, the heat sink includes: a first metal block having the channel grooves and the fins; and a second metal block which is joined to the first metal block so as to cover the fins of the first metal block.
In accordance with a fifteenth aspect of the present invention, in the thirteenth aspect, each of the fins of the heat sink is provided with slopes at its both ends.
In accordance with a sixteenth aspect of the present invention, in the thirteenth aspect, the width of the channel groove in the heat sink is set to 0.05 mmxcx9c0.4 mm.
In accordance with a seventeenth aspect of the present invention, in the sixteenth aspect, the width of the channel groove in the heat sink is set to 0.2 mmxcx9c0.25 mm.
In accordance with an eighteenth aspect of the present invention, in the thirteenth aspect, the length of the channel groove in the heat sink is set to the length of the IC chip or more.
In accordance with a nineteenth aspect of the present invention, in the eleventh aspect, the thickness of the heat sink is set to 1 mm or less.
In accordance with a twentieth aspect of the present invention, in the eleventh aspect, the semiconductor device further comprises a forcedly air-cooled radiator for cooling the coolant.